Filtering apparatus are used for a wide variety of purposes, most of which involve separating a substance, e.g., particulate matter, from a "medium" with which the substance is mixed. Certain types of such filtering apparatus are used to separate particulate matter from a flowing medium, e.g., air or water.
Examples of types of filtering apparatus used for water filtration are shown in U.S. Pat. Nos. 4,507,200 (Meissner); 3,988,244 (Brooks) and 5,190,651 (Spencer). Such apparatus, widely applied for filtering water in swimming pool and spa applications, incorporate a rigid outer enclosure or housing having connections for delivering water to and receiving water from such housing.
Confined within the housing is a filter cartridge of the type shown in the Spencer patent or the Brooks patent noted above. Such cartridge has a structural filter component embodied as a perforated, substantially rigid support core having a serpentine flow path along its length. A permeable filter element made of pleated cloth, paper or the like is mounted so that such element contacts the core. Because there is a pressure differential across the element (sometimes referred to as a "pressure drop") while liquid is flowing through it, there is a tendency for the element to deform or collapse. The core supports the element and prevents such deformation or collapse.
In the arrangements shown in the aforementioned Spencer and Brooks patents, the core is interposed between two concentric filtering elements. Top and bottom end caps are permanently attached to the elements and to the core to form a hollow, tube-like cartridge. It is not uncommon to encounter cartridges which are quite substantial in size, i.e., about nine inches in diameter and more than eighteen inches in length.
Water pumped into the housing flows radially outward through the inner element and radially inward through the outer element as it is filtered. The filtered water then flows downward along the serpentine path in the core and thence to an exit port in the housing. The leading manufacturer of such housings, filter cartridges and other water-filtration apparatus for pool and spa use is Sta-Rite Industries, Inc. of Milwaukee, Wis.
While such arrangements have been generally satisfactory for their intended purpose, they have certain characteristics which some users view as disadvantageous. For example, the bottom end cap of a filter cartridge of the type described above fits snugly into an annular slot or groove formed in a housing base and seals along the groove edges. Such sealing is needed to prevent water from "bypassing" the cartridge.
When the user desires to withdraw the cartridge from the base for cleaning or replacement, it is necessary to manually overcome this "frictional" snug fit. In a larger cartridge, this can require significant "lifting" force.
Yet another disadvantage is that when the cartridge is waterlogged, it is heavy--and in the case of a larger cartridge, it is very heavy. For that reason alone, it may be difficult for an infirm or slightly-built person to lift and remove the cartridge from the housing. And the aforementioned frictional fit aggravates that problem.
Still another disadvantage is that, at least as to the inner element in a dual-element cartridge, such inner element is difficult to clean. This is so since the hole through the axial center of the cartridge is not sufficiently large to admit a person's hand while holding a garden hose. Hosing a filter element is the technique commonly used to wash collected particulate matter from the element surfaces.
Another disadvantage is that because the end caps, the core and the elements are all bonded together, it is not possible to gain access to those element surfaces which are adjacent to the core. Therefore, particulates which may be lodged on such surfaces cannot be removed (at least not readily removed) by hosing. A corollary disadvantage is that an element cannot be easily "backwashed" by flowing pressurized water through it in reverse direction. The pool or spa pumping system is usually not arranged to permit "inside out" or reverse water flow and access for hosing purposes cannot be gained to those element surfaces adjacent to the core.
Another disadvantage is that because of their inherent shape, cylindrical filter cartridges waste significant amounts of storage and shipping space. If they are boxed (as they typically are), there are wasted spaces between the cartridge and the box corners and at the center cavity of the cartridge itself. If they are loose (much less typically), it is not possible to place multiple stacks of cylindrical filter cartridges without having unusable, relatively-large-area interstices between them.
Yet another disadvantage is that if one of the 10 filtering elements because damaged, e.g., torn or the like, it can no longer effectively filter water. In that event, the entire cartridge must be discarded and replaced. Doing so involves unnecessarily discarding the central core (which is rarely damaged) as well as discarding the end caps and intact filtering element.
An improved filter apparatus overcoming these disadvantages would be an important advance in the art.